1. Field of the Invention
The invention relates generally to the field of aeronautical navigation, and in particular to estimation of wind velocity.
2. Background Information
A need exists to accurately, efficiently and economically estimate wind velocity relative to an aircraft and/or the ground using outputs from an Inertial Navigation System (INS) and/or a Global Positioning System (GPS) instrument on board the aircraft.
In accordance with an exemplary embodiment of the invention, a method for estimating a velocity of a fluid (e.g., air) in three dimensions relative to a first object (e.g., an aircraft) in the fluid and/or relative to a second object (e.g., the earth or an object in fixed position relative to the earth), includes determining an acceleration of the first object relative to the second object. The method further includes determining a dynamic pressure of the fluid on the first object, determining a thrust vector of the first object relative to the second object, and determining the velocity of the fluid relative to the second object in the three dimensions, based on the determined acceleration, the determined dynamic pressure, the determined thrust vector and an assumption that a speed of the fluid along the third dimension is nominally zero.
In accordance with another exemplary embodiment of the invention, a method for estimating air velocity of a vehicle includes determining a parameter associated with the vehicle, determining a weighting factor to weight each equation in the equation set, based on the determined parameter, and solving the weighted equation set to estimate the air velocity of the vehicle.
In accordance with exemplary embodiments of the invention, the attitude, ground velocity, and acceleration inputs from an aircraft Inertial Navigation System (INS) and/or a Global Positioning System (GPS) instrument on board the aircraft, are used to estimate wind velocity relative to the aircraft and/or the ground in three dimensions. In an exemplary embodiment of the invention, one or more of a) atmospheric density, b) speed of sound, c) air temperature, d) thrust of the aircraft, e) aerodynamic force coefficients of the aircraft, and f) mass of the aircraft, are used in conjunction with the inputs from the INS/GPS instrument(s) to estimate the wind velocity. Air temperature can be used, for example, together with an ambient air pressure and/or a known altitude of the aircraft to indicate an atmospheric density.
The estimate of wind velocity can be desirable, for example, to help an autopilot keep the aircraft stable and guide the aircraft to a destination or waypoint, and to estimate pitch and yaw of the aircraft relative to the airmass through which it is moving. The estimate of wind velocity can also be used to determine an aerial dispense point of free-falling submunitions so that the submunitions will arrive with a desired accuracy and/or pattern at a target or target zone.